Many types of input devices are available for performing operations in a computing system, such as buttons or keys, mice, trackballs, touch sensor panels, joysticks, touch pads, touch screens, and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned behind the panel so that the touch sensitive surface can substantially cover the viewable area of the display device. Touch screens can generally allow a user to perform various functions by touching or near touching the touch sensor panel using one or more fingers, a stylus or other object at a location dictated by a user interface (UI) including virtual buttons, keys, bars, displays, and other elements, being displayed by the display device. In general, touch screens can recognize a touch event and the position of the touch event on the touch sensor panel, and the computing system can then interpret the touch event in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event.
Because typical touch screens have the touch sensor panel overlaying the display device, the touch screens can be heavier, thicker, and dimmer. A lighter, thinner, and brighter touch screen has been developed in which the touch sensor panel is integrated with the display device to provide both display and touch capabilities. Such a touch screen is described in U.S. patent application Ser. No. 11/760,080, entitled “Touch Screen Liquid Crystal Display,” and U.S. patent application Ser. No. 12/240,964, entitled “Display with Dual-Function Capacitive Elements,” the contents of which are incorporated herein by reference in their entirety for all purposes.
However, because of the dual capabilities of the touch screen, it can be difficult to effectively detect touch on the screen when executing the touch capabilities due to interference, e.g., parasitic capacitance, from the display circuitry. More expense and power could be needed to provide a more robust touch signal that can overcome this difficulty.